How to make sure your roommate doesn’t take too long in the shower? You have them stabbed, but in a gentle manner, of course. Six years ago, London-based artist Elisabeth Buecher created a clever contraption that kicks you out of the shower using plastic spikes.

Called ‘Spiky’, the curtain goes off after four minutes, hitting you with its spikes and abruptly ending your horrible shower singing. It was made to make sure you don’t waste water with unnecessarily long showers....